1. Technical Field
The present invention relates generally to image compression, and more specifically relates to a black white image data compression system and method having print density control.
2. Related Art
Since the advent of the modem information technology age, systems have been developed to store, process, or communicate black white image data retrieved from printed documents. Common examples include, for instance, facsimile machines, copiers, scanners, etc. In many instances, the system is required to archive, store or transmit the black and white image data. To improve performance, the image data is compressed, thereby reducing storage, processing and bandwidth requirements.
Black white image data compression techniques are well known in the art. Due to the universal need for encoding and decoding (namely compression and decompression) of image data, the industry has adopted standards, which are widely used today. CCITT-G4, for example, is one of the most popular standards, finding its most extensive use in facsimile machines. Typical compression ratios using CCITT-G4 are on the order of 10-15×. Ultimately, the amount of compression is a function of the black white image information/data content.
In the case of most black white compression standards, such as CCITT-G4, the compression process, which is engineered to be an encoding process, is lossless, i.e., following the decompression process, all information present in the original image is fully recovered. Limitations exist with respect to the amount of compression that can be achieved.
Numerous present day industries are increasingly required to archive vast amounts of information in electronic form. Examples include the finance industry saving check images, the insurance industry saving documents, the health care industry saving medical records, the legal industry, federal and state governments, etc. Accordingly, in order to reduce storage costs, data compression for black white images remains of vital interest.
Often, it is not necessary for the compression to be completely lossless, i.e., some minor compression errors may be acceptable so long as the pertinent information contained on the document is not lost. For instance, imperfections on a compressed bank check image may be acceptable as long as legibility of the important information, e.g., name, amount, account, etc., is not impacted by the compression. An image compression system that could also enhance legibility of important information would be of great use for industries seeking black white image compression.